A．Clear glass was easier to find than quartz.
B．Clear glass was easier to cut to the appropriate size.
C．Clear glass magnified the letters more than quartz did.
D．Clear glass was less expensive than quartz.

A．Its historical records are more detailed than those of other inventions.
B．It has little impact on social attitudes toward vision correction.
C．Its occurrence in different places at approximately the same time is not unusual.
D．It contributed to a substantial increase in the number of literate people.

A．They were available to everyone.
B．They were a symbol of wealth and wisdom.
C．They could not correct vision accurately.
D．They could be bought only in the big market.